The present invention relates to compositions useful for oxygen scavenging. The invention also relates to substantially transparent compositions that comprise a base polymer, an oxidizable organic component, and a transition metal in the positive oxidation state. The invention also is directed to uses of such compositions in the construction of packaging for oxygen sensitive materials.
All references, including publications, patent applications, and patents, cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein.
It is known in the art to include an oxygen scavenger in the packaging structure for the protection of oxygen sensitive materials. Such scavengers are believed to react with oxygen that is trapped in the package or that permeates from outside of the package, thus extending to life of package contents. These packages include films, bottles, containers, and the like. Food, beverages (such as beer and fruit juices), cosmetics, medicines, and the like are particularly sensitive to oxygen exposure and require high barrier properties to oxygen to preserve the freshness of the package contents and avoid changes in flavor, texture and color.
Use of certain polyamides in combination with a transition metal is known to be useful as the oxygen scavenging material. One particularly useful polyamide is MXD6 which contains meta-xylene residues in the polymer chain. See, for example, U.S. Pat. Nos. 5,639,815; 5,049,624; and 5,021,515.
Other oxygen scavengers include potassium sulfite (U.S. Pat. No. 4,536,409), unsaturated hydrocarbons (U.S. Pat. No. 5,211,875), and ascorbic acid derivatives (U.S. Pat. No. 5,075,362).
U.S. Pat. Nos. 6,083,585 and 6,558,762 to Cahill disclose the oxygen scavenging polyester compositions wherein the oxygen scavenging component is polybutadiene and the catalyst for the oxygen scavenging material is transition metal salts.
U.S. Pat. No. 6,423,776 to Akkapeddi discloses the use of oxidizable polydienes or oxidizable polyethers as oxygen scavengers in blends with polyamides.
U.S. Pat. No. 6,254,803 to Ching discloses the use of polymers having at least one cyclohexenyl group or functionality as oxygen scavengers.
In barrier layers of packaging walls that are made from blends of a polymeric oxygen scavenging material such as that described in all of the above prior art, in a base polymer resin such as PET, an undesirable haze can result due to the immiscibility of the polymeric scavenging materials in PET. It is a well known fact that blends of polymers of dissimilar chemical structures invariably results in phase separation due their mutual segmental incompatibility. Phase separation is the root cause for the haze in such blends.
One approach to minimize the haze in polymer blends is the use of compatibilizers or interfacial agents which improve the dispersability of the polymeric scavenger in the base polymer. However this approach, while it may reduce somewhat, does not eliminate the haze and hence the desired high clarity is not achievable. Thus, there is a need in the art for improved materials such as lower molecular weight organic compounds or oligomers which provide high oxygen scavenging capability when blended into PET to form containers while maintaining substantial transparency. In principle, low molecular weight organic compounds of adequate polarity are capable of being miscible in base polymers such as PET due to their molecular size allowing them to penetrate into the free volume that exists between the base polymer chain segments and remain truly soluble due to favorable molecular interactions. Similarly polar organic oligomeric materials having a sufficiently high molecular weight (MW>400) for non-migratability from PET, yet having a sufficiently low molecular weight (i.e., MW of <4000) to prevent phase separation, are expected to be nearly miscible in PET.
Besides appearance, another problem experienced with prior art oxygen scavengers is that once they are incorporated into plastic containers, they require an induction period (i.e., time delay) before the onset of oxygen scavenging. For example, molded containers that employ diamides such as, for example, dibenzyl adipamide (DBA) as oxygen scavengers, the induction period can be at least three months at ambient temperature and humidity or at least four weeks at elevated temperature (38° C.) and humidity (85% RH) after the bottles are filled with deoxygenated water. This induction period is not acceptable in real commercial practice where plastic containers are made and filled immediately (or shortly thereafter) with an oxygen-sensitive food or beverage product. The oxygen scavenging must occur immediately after filling to protect the taste and nutrient qualities of the food and/or beverage products contained within.
Thus, there is a need in the art for effective oxygen scavenging compositions that satisfy container clarity requirements and eliminate any induction period for oxygen scavenging such that prolonged aging or conditioning of formed containers is not needed.